Fluent NHibernate mapping class within the entity class

Question

I'm studying Fluent NHibernate now, and have a question about mapping. It's not an issue, but a best practice question.

I know that with Fluent NHibernate there is a new fluent mapping, and it requires a new Class for mapping fields that will be used by the Entity Class. I was wondering, if the Mapping Class is directly linked to the Entity Class (It will map exacly for the entity class), do best practices dictate that they can't be joined within the same .cs file? Please note that there will be no nesting here.

I.e.: There are Product and a ProductMap classes, both for a Product table on my database, so I'd place both classes within the same Product.cs, like the following:

namespace Business.Entity
{
    public class Product
    {
        ...
    }

    public class ProductMap : ClassMap<Product>
    {
        ...
    }
}

If the classes shouldn't be inside the same file, would you care to explain why, and maybe with real examples?

Thanks in advance!

score 1 · Accepted Answer · answered Sep 03 '12 at 17:13

When creating the SessionFactory instance, you will pass a class that tells which assembly has the mapping definitions. Then, using reflection, it'll iterate through all the classes on this assembly that inherit from ClassMap<T>.

That said, for a faster initialisation, it's better to have this assembly as light as possible, and it means that it would be better to have an assembly that would hold only the mappings and not the classes definitions.

AFAIK this is the only difference. Any feedback will be appreciated.

score 1 · Answer 2 · answered Sep 03 '12 at 17:14

1

You should design your entities persistant ignorant as much as possible.

That means you shouldn't make Product derive from ClassMap<Product>. But it also means that the ProductMap shouldn't even be in the same project as your entity.

Typically, you would have a DAL project that contains the mapping and a Domain / Business project that contains the entity

answered Sep 03 '12 at 17:14

Daniel Hilgarth

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I'm familiar with this DAL/Business layering, and it makes more sense to put the mapping inside the DAL layer, or even separated cosnidering the answer provided by @Andre-Calil – Alexandre Fernandes Sep 03 '12 at 17:24
`Product` won't ever inherit from `ClassMap`, it makes no sense. The point here is where to place the mapping classes. And looks like we all agree that they should be on an exclusive class library. – Andre Calil Sep 03 '12 at 17:36

score 1 · Answer 3 · answered Sep 04 '12 at 17:34

You can keep both classes in different files, even in different namespace. but if you are beginner then you can keep entity class in different file and map class in different file within same namespace.

/* Product.cs */
namespace Business.Entity
{
    public class Product
   {
    ...
   }
}

/* ProductMap.cs */
namespace Business.Entity
{
    public class ProductMap : ClassMap<Product>
    {
    ...
    }
}

Fluent NHibernate mapping class within the entity class

3 Answers3